over the weekend i gave that spring action M16 a look. and only to realize that there's no hop up. >.<! bummer.
anyway, here's a rough picture of my problem
at 10-12ft the bb still fly straight and i manage to hit every target with little effort. not to mention that the bb punch a hole through a cardboard box
at 15ft this is my results.
it still pack a punch and you can see that it's skewed to the right.

center = cross hair
red = bb shots
20ft, i noticed that the bb fly at a curve and missed the target entirely.
I thought it was the iron sight, but it's fixed dead on the barrel and non adjustable. at 10-12ft bbs hit dead center, so could not be the iron sight.
so, without hop up adjustment, is it possible to fix this stray shooting M16?